Worried about dropping dead if you run a marathon? Researchers in Canada say you can put your mind at ease. The risk of dying on a marathon course is twice as high if you drive it than if you run it, they find.

In fact, they conclude, marathons may actually save lives: more people would die in traffic accidents if the race course had not been closed to vehicles on marathon day. (Nor was there any spillover of extra deaths on alternative routes.) Their paper is being published Friday in The British Medical Journal.

“For each death in a marathon, two motor-vehicle crash deaths were averted,” said Dr. Donald A. Redelmeier, a professor of medicine at the University of Toronto and the lead author of the new study. “It’s riskier if you decide to drive your car around on a Sunday morning than if you go out and run.”

As might be expected, marathon directors were pleased.

“That’s a very positive piece of news,” said Guy Morse, executive director of the Boston Athletic Association, which organizes the Boston Marathon. He hastens to add that there have been very few deaths in that marathon — just two, in fact, since the 1970s.

Dr. Paul Thompson, a marathon runner and a cardiologist at Hartford Hospital who has studied the risk of having a heart attack or dying in a marathon, called the new study “a unique perspective,” and added, “It looks at deaths from a societal point of view.”

The researchers admit that they cannot prove marathons saved lives. They were comparing actual deaths during marathons to expected deaths from motor-vehicle accidents based on statistics. But they add that their data certainly raise the question of whether the risk of dying in a marathon is exaggerated.

Dr. Redelmeier, who has run a marathon, said he began his study out of annoyance with the enormous attention given to each death in a marathon — often even greater, he added, than the attention paid to the winner. When someone died in the Toronto Marathon, he said, there were immediate calls to close it down.

“It has a chilling effect,” he said, “and becomes one more excuse not to exercise.”

So he and his colleagues decided to examine data from 26 American marathons over 30 years. They included results from 3,292,268 runners on 750 race days and 14 million hours of running. For comparison, they also examined national data on traffic fatalities, estimating how many would be expected to occur in the area on marathon day and comparing that with the number that did occur.

Fewer than 1 in 100,000 people died while running a marathon, Dr. Redelmeier and his colleagues reported. The chance that a middle-aged man — the typical marathon fatality — would die while running a marathon was about the same as the chance a middle-aged man would suddenly die anyway.

Dr. Thompson, the Hartford cardiologist, said there was another way of making the comparison. He noted that middle-aged men who run marathons are not typical of men their age. He said their risk of dying while running a marathon, while low, was nonetheless about seven times their risk of dying at other times.

Dr. Redelmeier also said his results did not depend on the marathon — some, like the one in Boston, have rigorous entry criteria for most runners and so tend to have a fitter group of athletes. Some are run in the heat, others in the cold. On some the course is flat, and on others it is hilly. The death rate, on average, was the same low number.

The study also found that half the people who died in a marathon did so while running the last mile and almost no deaths occurred in the first 13 miles.

Dr. Redelmeier says he took his own results very seriously. He is not a fast runner, but when he ran a marathon in Lake Placid, in 4 hours 17 minutes, he deliberately kept his speed down in the last mile.

“I kept cool,” he said. “That takes a lot of self-control. I have this fragile male ego.”